An orthogonal frequency division multiplexing (OFDM) technology features strong multipath interference immunity, simple implementation of discrete Fourier transform, facilitating a multi-antenna transmission technology, and the like, and therefore, is widely applied to downlink signal transmission in an LTE system.
The OFDM technology is based on a multicarrier system. Therefore, a peak to average power ratio, referred to as a peak to average power ratio (PAPR) for short, of the OFDM technology is high, and a requirement on linear power amplification of a transmitter is very high. There is a low requirement on cost control on a base station side, and a transmitter having high power amplification linearity can be used. Therefore, the OFDM technology is usually used in downlink transmission. However, UE has limited transmit power and is cost-sensitive, a requirement on power amplification of a transmitter needs to be lowered, and coverage of the UE needs to meet a particular requirement. Therefore, a single carrier frequency division multiple access (SC-FDMA) technology is usually used in uplink transmission. Compared with the OFDM technology, the SC-FDMA technology has a lower PAPR, and can lower the requirement on power amplification of a transmitter, and improve power utilization.
An SC-FDMA solution used by a current LTE system is a discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) technology. The DFT-S-OFDM technology can achieve peak PAPR performance close to that of a single-carrier signal. Based on a low PAPR, hardware implementation complexity and costs can be reduced. When subcarrier groups occupied by different users are non-overlapping, the DFT-S-OFDM can implement orthogonal frequency division multiple access, to obtain a single-carrier orthogonal frequency division multiple access solution. Therefore, the DFT-S-OFDM technology is particularly applicable to uplink transmission of a mobile communications system.
In a current DFT-S-OFDM technology, for transmission of a plurality of signals or channels of one UE, to maintain PAPR performance close to that of a single-carrier signal, an uplink data signal and an uplink reference signal (such as a demodulation reference signal (DMRS)) are transmitted in a time division multiplexing manner.
On the other hand, a short-TTI feature is introduced to LTE Release 14 (Release 14, R14), and a shortest TTI may be a symbol. With the short-TTI feature, one symbol may need to carry both a reference signal and a data signal.
An example is used for description: One uplink symbol carries both a DMRS and a physical uplink control channel (PUCCH), and the DMRS and the PUCCH are orthogonal through code division multiplexing. In frequency domain, the DMRS and the PUCCH use different phases of one base sequence (base sequence) to map to a same group of subcarriers. The different phases of the base sequence are orthogonal. It should be noted that, different phases of one base sequence in frequency domain correspond to different cyclic shifts for the base sequence in a time domain sequence. If the different phases of the base sequence in frequency domain are orthogonal, different cyclic shifts for the base sequence in time domain are also orthogonal. In this specification, a representation of a base sequence in frequency domain is referred to as a frequency domain base sequence, and a representation of a base sequence in time domain is referred to as a time domain base sequence.
Specifically, assuming that a signal obtained by performing code division multiplexing on a DMRS and a PUCCH is sent on one symbol, and an occupied frequency domain resource is one resource block (RB), a length of a base sequence is 12, the DMRS and the PUCCH use two different phases of the base sequence, and a frequency domain signal obtained through code division multiplexing is expressed as:S(n)=rx(n)ej2πα1n/12+d(m)rx(n)ej2πα2n/12,n={0, . . . ,11},
where rx(n) is a base sequence having a length of 12 obtained through quadrature phase shift keying (QPSK) modulation, α1 and α2 are selected from the 12 phases, α1−α2 is not equal to 0, and d(m) is a symbol obtained by performing QPSK modulation on 2-bit information carried on the PUCCH sent on the symbol.
In the foregoing example, because a signal sent on one symbol is a signal obtained by superposing sequences that are obtained by rotating a plurality of phases of one base sequence, and a composite signal S(n) is no longer an SC-FDMA signal, compared with the SC-FDMA signal, a PAPR increases. Consequently, power utilization is reduced, and performance of an up link is affected.